A secondary battery includes an electrode laminated body contained in an outer case. The electrode laminated body is produced in such a way that positive and negative electrode sheets are wound in a flat shape or stacked in flat layers by interposing separators therebetween. Each of the electrode sheets is made of a sheet-like collector foil formed, on its both surfaces, with active material layers.
To connect the electrode laminated body and an external terminal, conventionally, a collector terminal is provided. Specifically, the collector terminal is placed to extend through the outer case to electrically connect the electrode laminated body located inside the outer case to the external terminal located outside the outer case. The electrode laminated body and the collector terminal are usually bonded to each other by resistance welding conducted by passing an electric current through their portions to be bonded together while bringing the portions in pressure contact with each other. Examples of such bonding technique are disclosed in Patent Documents 1 and 2.
In the technique of Patent Document 1, a collector member (a collector terminal) is connected to a substrate exposed portion (a collector foil) of an end portion of a flat wound electrode body (an electrode laminated body). To be concrete, the substrate exposed portion consisting of overlapping parts of the foil is divided into two in an overlapping direction, and a current carrying block is placed between the divided two parts. Further, collector members are put on both outermost surfaces of the substrate exposed portion on both sides of the current carrying block. Thus, the collector member and the substrate exposed portion are connected by resistance welding and the substrate exposed portion and the current carrying block are connected by resistance welding (two points in each case). The current carrying block used thereof is a block formed with a protrusion which will be bonded to the substrate exposed portion. This protrusion is to be melted during resistance welding.
In the technique of Patent Document 2, a substrate exposed portion of a wound electrode body is held or clamped from both surfaces by a collector and a collector receiving part (a pair of collector terminals) in a direction of flat overlapping parts of the exposed portion, and the overlapping parts are bonded to each other by resistance welding. At least one of the collector and the collector receiving part is formed with a protrusion which will be bonded to the substrate exposed portion. This protrusion is to be melted during resistance welding.